Many balance assessments are conducted in standing even though the majority of falls occur during locomotion. Since the mechanisms underlying stability for standing and walking are different', balance should probably be assessed during motion as well as in standing. There is no agreed upon measure of balance during walking;indicators of variability, stability and smoothness have all been used to reflect postural control during walking. Gait variability, stability, and smoothness have all individually been associated with reductions in locomotor function[2-6], but the three indicators appear to capture different aspects of mobility and balance, and may provide unique and complementary information.[6] The relationships among the three in terms of implications for balance are unknown. The objective of this project is to, for the first time, study postural control during walking (dynamic balance) by simultaneously quantifying variability, stability and smoothness, and comparing them to standing sway in i) three groups with distinct balance abilities and 2) between task conditions likely to affect balance in distinct ways. In order to assess contrasting effects due to the of balance disorder, we will study 10 healthy older adults (controls), 10 older adults vdth mild to moderate Parkinson's disease (PD) and 10 older adults with peripheral neuropathy (PN).7-9 In order to assess contrasting effects due to task conditions, we will assess normal pace walking, slow walking and dual task walking. SPECIFIC AIM 1 Evaluate which measures of balance best discriminate among groups of older adults with known differences in balance. Hypothesis la: During usual walking, all three measures of dynamic stability will discriminate among the three groups and the marginal explanatory power will remain after controlling for standing sway. Hypothesis lb: During usual walking, stance time variability will discriminate PN from controls and smoothness will discriminate PD from controls. SPECIFIC AIM 2: Evaluate which measures best discriminate the effects of task condition. Hypothesis 2a: Stability will best detect change in performance from usual to slow walking. Hypothesis 2b: Variability will best detect change in performance from usual to dual task walking. Exploratory Aim: Data from this pilot will also be used by Developmental Project 3 (Perera and Loughlin) to develop further measures of gait variability. The major contribution of the findings from this pilot study is to better understand how to use different measures of dynamic balance to assess changes with aging and disease. This study supports the goals of the OAIC to improve and retain mobility and balance function in older adults by simultaneously assessing multiple indicators of balance, so we can begin to build a comparative knowledge base of how to use and interpret measures in future research, which should in turn inform studies of causation, prevention and treatment.